1. Field Of The Invention
The present invention relates to a downhole tool for use in oil or gas wells, or the like. This tool is constructed to perform what is known as a "well surging operation" where formation fluid from a zone of the well is rapidly surged out of the formation and into the well to clean debris away from the inner surfaces of the formation and to clean debris from perforations in the well. The tool has pressure actuated ball valves and a backup means for mechanically actuating the upper one of the valves.
2. Description Of The Prior Art
The prior art includes systems for performing surging operations on a well. Any of these prior art systems generally utilize either rupture disks or flapper-type valves to rapidly replace the producing formation in communication with a low pressure chamber in the tool, so that fluid from the well formation will rapidly flow into the tool. One of the most commonly used prior art systems includes a rupture disk which is ruptured by the thrusting action of a plunger.
Although such prior art techniques produce a dynamic surging effect and acceptable drawdown of the producing formation of the well, pieces of the disk itself will sometimes clog choke valves and other rupture equipment connected to the valve after the disk has ruptured. Such a condition most often occurs when the disk does not shatter into fine enough pieces to be circulated out of the well.
Another unfavorable condition that sometimes occurs with these prior art systems is when the disk itself does not completely detach, and instead acts somewhat as a flapper valve in the inner bore of the drill pipe. Under that circumstance, difficulties are presented in circulating fluid upwardly through the drill pipe, due to the flapper valve effect of the partially severed rupture disk. In such situations, the less desirable method of circulating fluids up through the well annulus has to be utilized.
Additionally, the materials, such as aluminum, from which the rupture disks are often constructed are not totally reliable when utilized in corrosive environments. Actions of corrosives weaken the rupture disks and quite often operators experience premature rupture of the disk.
Thus, there has been a need for a well surging system which can provide rapid communication of the well zone with a low pressure chamber, so as to achieve the required rapid surging of fluid from the well zone into the low pressure chamber, and yet avoid the various problems associated above with rupture disk type systems. One such device which has been developed to address this problem is disclosed in U.S. Pat. No. 4,619,325 to Zunkel, assigned to the assignee of the present invention. This well surging system includes an elongated housing assembly having a central flow bore disposed therethrough. Upper and lower independently pressure actuated ball valves are disposed in the housing assembly. Each of the ball valves is independently movable between a closed position wherein the flow bore is closed and an open position wherein the flow bore is open. The upper and lower ball valves define a low pressure surge chamber therebetween when the ball valves are in an initially closed position. This surge chamber is actually a portion of the flow bore.
In the Zunkel apparatus, a packer means is connected to the housing assembly for effectively sealing a well annulus below the housing assembly and a well bore so that a well zone below the packer may be surged.
A lower ball valve operating means is provided in the prior apparatus for opening the lower ball valve prior to opening of the upper ball valve means. When the lower ball valve is opened, well fluid from the well zone surges upwardly through the flow bore of the housing assembly past the opened lower ball valve into the surge chamber. An upper ball valve operating means is provided for opening the upper ball valve after the lower ball valve has been opened. When the upper ball valve is opened, well fluid in the surge chamber may then be circulated upwardly through a bore of a tubing string connected to the well surging apparatus.
This prior art well surging system has worked well, but if for some reason the upper ball valve does not operate with pressure, there is a need to mechanically actuate the apparatus. The present invention provides such a mechanical backup means.